This invention relates to tamper evident closures for containers and in particular to tamper evident closures which undergo a permanent, visible change on first opening of the container.
Many forms of tamper evident closures for containers are known, made in plastics, metals or a combination of the two. Such closures have a part the condition and/or position of which indicates that the closure has been removed from the container, or at least an attempt to remove it from the container has been made.
Many of these closures have two parts which are formed separately and then assembled together after manufacture. However, closures of this kind tend to be relatively expensive, in particular because of the assembly operation. Also there is the possibility of tampering by separating the parts of the closure to overcome the tamper evidence.
It is also well known to provide a tamper evident closure with a portion which is partially or wholly severed from the remainder of the closure to provide the tamper evidence. Closures of this kind include those in which the free edge of the closure skirt is formed as a security ring which is attached to the remainder of the skirt by frangible bridges. The security ring breaks partially or wholly away from the closure at these bridges when the closure is first opened. A further kind of closure has relatively movable inner and outer shells, the outer shell of which has a portion formed in its crown or closure panel which is arranged to be partially or wholly severed when the shells are moved axially in relation to one another. A closure of this latter kind is disclosed in U.S. Pat. No. 4,527,701.
U.S. Pat. No. 5,738,231 discloses a threaded tamper indicating closure which provides an indication of initial opening by how far the closure threads onto a container neck.
However, the tamper evident closures discussed in the previous paragraphs have several disadvantages. For example, they may be environmentally unsatisfactory and are often unsightly and/or uncomfortable to use after they have been opened for the first time. They may also require modification of the container to which they are to be fitted. Furthermore, it may be possible for a tamperer to overcome the tamper evidence by opening the closure, breaking the frangible portion, and then reinstating the closure on the container in a substantially undetectable manner.
A plastics moulding technique which has been used to a limited extent in the manufacture of packaging components is commonly referred to as xe2x80x9csequential mouldingxe2x80x9d. In this process a plastics pre-article or xe2x80x9cpreformxe2x80x9d is first moulded by introducing hot, possibly molten, polymer into a correspondingly shaped (and appropriately dimensioned) cavity defined by a mould, causing the polymer to conform to the mould cavity and thereafter allowing the polymer to cool and solidify. The mould cavity is then opened, leaving the preform still held on a part of the mould, and that mould part and the attached preform is used to create a new mould cavity in which the preform forms a part of the defining wall. A second hot polymer, which may differ from the first, is then introduced into and conformed to the new mould cavity, so that after cooling an article having two intimately associated parts is formed. The article is subsequently ejected, possibly after one or more additional sequential moulding operations have been performed upon it. Usually, the moulding operations are each performed by injection-moulding, with molten polymer introduced into the mould cavity at high pressure, or by compression moulding, with the second part being moulded into the shell of the preform.
The present invention is based on the realisation by the Applicants that, especially by the use of sequential moulding, a tamper evident closure can be produced from which some or all of the disadvantages of the known closures recited above are eliminated, to at least a significant degree.
Accordingly, the invention provides a tamper-evident closure for a container, comprising first and second plastics parts adapted to move relative to one another from an initial position to a new limiting position which is visually distinguishable from the initial position, characterised in that at least a portion of the first and second plastics parts have complimentary formations including a re-entrant section, and in the initial position the plastics parts are moulded in mutually intimate association by sequential moulding and, on first opening of the closure, the complimentary formations are adapted to disengage and thereafter cannot be re-engaged. An advantage of sequentially moulding the first and second plastic parts is that they may be provided with complimentary formations which are intimately inter-engaged in the as-moulded position, but which become disengaged, and are difficult or impossible to re-engage, once the two parts are separated for the first time. The difficulty in re-engaging the complimentary formations is enhanced by selecting a suitable shape for the complimentary formations. The invention has application to tamper evident screw and snap-on closures of the kind which are removed when it is desired to dispense product from the container. Such a closure may comprise the first and second plastic parts as relatively inner and outer closure parts respectively.
The closure may further include an outermost, metal part within which the inner and outer closure parts are disposed. Preferably, in the manufacture of such a closure the outer closure part is formed directly within the metal part by insert moulding, the inner closure part being subsequently formed by sequential moulding within the outer closure part. Alternatively, the inner and outer parts may be formed as a discrete component which is subsequently bonded and/or mechanically secured in the metal part.
xe2x80x9cInsert mouldingxe2x80x9d, as referred to in the previous paragraph, is a form of moulding in which an article is placed into a mould as an insert, to define part of the wall of the mould cavity, hot polymer is introduced into and conformed to the mould cavity and then caused to cool and solidify. In the composite article so produced the moulded polymer is in intimate association with the insert, and may be strongly bonded to it at the interface between them.
The invention may also be applied to dispensing closures, that is to say closures which are held captive on the container and arranged to dispense product through a dispensing orifice which is opened and closed by relative movement between the two parts of the closure. Usually such closures have a first, body part which is attached to the container by screw or snap-on engagement. The second part is provided as a lid, which co-operates with a dispensing orifice in the body part and is usually hinged to the body part of the closure. In known closures of this type, the lid and body parts may be moulded as a single piece, with the lid and body parts connected together by a film hinge.
An advantage of using sequential moulding to form such hinged dispensing closures is that the film hinge may be replaced by a mechanical hinge, without the addition of the assembly operation usually inherent with use of this type of hinge. Mechanical hinges have the advantage that they are generally more robust than film hinges and thus are less likely to break. For example, the pin of the hinge may be moulded integrally with the first, body part of the closure. The lid may then be sequentially moulded with the sleeve portion of the hinge moulded integrally with the lid.
Use of sequential moulding to form a dispensing closure also has the advantage that different materials may be used for the body of the closure and the lid. This allows the lid to be made from a softer, more flexible material, which in turn helps the sealing performance of the closure where the lid co-operates with the dispensing orifice. Such softer materials are unsuitable for making a film hinge as they break too easily.
Alternatively, the outer part of the closure may be made from a harder material to provide abuse and scuff resistance and the inner part of the closure may be made from a softer material to provide a good seal both against the body and the lid.
This technique is particularly useful for forming a closure on a tube, such as a toothpaste tube for example. The ability to use two different materials means that the body of the closure may be made from polyethylene so that it can bond to the tube, whilst the lid may be provided in polypropylene to provide a robust mechanical hinge.